Variable voltage wave form generator



July 1954 e. D. PAXSON VARIABLE VOLTAGE WAVE FORM GENERATOR 2Sheets-Sheet 1 Filed May 6, 1953 INVENTOR.

GORDON DONALD FMXSON 25.2mm mmnzo o ATTORNEK July 13, 1954 D PAXSON2,683,807

VARIABLE VOLTAGE WAVE FORM GENERATOR Filed May 6, 1953 2 Sheets-Sheet 25 8 V o Q 9 I INVENTOR.

GORDON DONALD PAXSON 8 0 BY w E A TTORNE Y.

Patented July 13, 1954 UNITED STATES PATENT OFFICE VARIABLE VOLTAGE WAVEFORM GENERATOR Commission Application May 6, 1953, Serial No. 353,402

2 Claims.

The present invention relates to an electronic voltage waveformgenerator and more particularly to a circuit for generating a voltagewaveform having a plurality of variable voltage points which may bevaried independently without disturbin the value of the voltage at otherpoints of adjustment of the waveform.

In certain applications of the synchrotron principles for theacceleration of charged particles, it is necessary that the frequency ofthe accelerating voltage vary at a predetermined rate with respect tothe rate of increase of the orbit confining magnetic field. To assuresuch relationship it has been found desirable to control the frequencyof the accelerating field by means of a voltage proportional to currentvariation in the excitation circuit of the magnetic field structure. Ina system of the foregoing type the requirements for accuracy are veryrigid thereby rendering the desired accuracy diflicult to attain becauseof the nonlinearity of interconnecting elements. To overcome the latterdifiiculty, the present invention permits the generation of a waveformof voltage which, when added to the voltage proportional to the magnetcurrent, overcomes variations from the required proportionality betweenthe frequency of the acceleration voltage and the magnetic fieldstrength.

It is therefore an object of the present invention to provide a new andimproved voltage waveform generator.

Another object of the invention is to provide a voltage waveformgenerator for developing a waveform having a plurality of variablepoints, each of which points may be varied without disturbing the valueof the other points.

A further object of the invention is to provide a voltage waveformgenerator having an output configuration comprising a plurality ofstraight, connected lines, the slopes of which may be varied.

Another object of the invention is to provide a voltage waveformgenerator responsive to an input signal whereby the input signal isdivided into a plurality of intervals so that the output for any of theintervals has a rate of change which is a positive or negative fractionof the input rate of change and the value of which starts at the valuewith which the preceding interval ended.

A still further object of the invention is to provide a voltage waveformgenerator responsive to an input signal whereby the input signal isarbitrarily divided into a plurality of intervals and the starting andendin values of the intervals are functions of the input signal only andindependent of time.

Other objects and advantages of the invention will be apparent in thefollowing description and claims considered together with theaccompanyll'lgdrawing in which:

Figure 1 is a schematic wiring diagram, partially in block form, of aportion of the present invention; and

Figure 2 is a schematic wiring diagram of the mixer and output circuitof the invention.

Referrin to the drawing in detail, Fig. 1 in particular, there areprovided a pair of input terminals H and i2, which for the purposes ofthe present invention may be connected externally of the circuit to asource of sawtooth voltages (not shown). Such input terminals H and I2are also connected to the input of a conventional diiferential amplifierl3 which provides a pair of output voltages between the terminals it andl i and the grounded terminal l8. The voltage between the terminals I6and I8 being of opposite phase from that between the terminals ll andi8. For convenience the polarity of the terminal It will be consideredas positive with respect to the grounded terminal [8 and the terminal l1negative with respect to such grounded terminal.

There is also provided a first conventional, regulated power supply 2|having a positive terminal 22 and a negative terminal 23, such polaritybeing respective. For the purposes of the invention there is no groundconnection to the power supply 2! so that the voltage between the twooutput terminals 22 and 23 is floating. To develop a plurality ofvoltage ranges of increasing value a plurality of resistors 24 areseriesconnected between the two terminals 22 and 23. Except for the endresistors 24, each of the other resistors has a separate potentiometer26 parallel-connected therewith so that adjustment is possible withineach voltage range. A further connection is made from the terminal 22 ofthe power supply 2! to the terminal it of the diiferential amplifier I 3whereby the floating voltage of the former is added to the voltage ofthe latter. I

A second regulated power supply 3|, similar to the first power supply2i, is provided having a negative terminal 32 and a positive terminal33. Again, there is no ground connection with respect to the powersupply 3i, so that the output voltage thereof is floating. There is alsoa voltage divider connected between the terminals 32 and 33 andcomprising a plurality of resistors 34 of which all but the oneconnected to the negative terminal 32 is parallel-connected with apotentiometer S6. A further connection is made from the negativeterminal 32 of the power supply 3! to the negative terminal i? of theamplifier G3 which results in the voltage of the former floating on thevoltage of the latter.

Interconnected between the above-described two voltage dividers of thepower supplies 2! and Bi are a plurality of identical units 41, a few ofwhich are illustrated in detail, some in block form, and some areomitted (see Fig. 1). Each of the units ii comprises in general acathode follower tube 52, a first diode tube as, and a second diode tube44. The anode of the tube i2 is directly connected to a first bus 46supplied with a positive potential from a power supply (not shown).Also, a connection is made from the cathode of the tube 42 through acathode resistor 4? to a second bus 58 supplied with a negativepotential from the power supply (not shown). To bias the tube 42 acurrent limiting resistor 49 is connected between the positive terminal22 of the power supply 2| and the control grid of the tube while thefirst diode'tube '53 is inserted in the circuit with the anode connectedto the control grid and the cathode to the adjustable element of thepotentiometer 35 which is closest to the negative terminal of the powersupply 3 i. The anode of the second diode tube at is directly connectedto the cathode of the tube 62 while the cathode of such diode tube isconnected to one end of a series-connected resistor and potentiometer52. The adjustable element of the potentiometer 52 is connected to athird bus 53 which carries the output of the circuit. The remainingunits ii are similarly connected between successive elements of the twovoltage dividers.

From the portion of the circuit described in the foregoing paragraphs,the bus 53 and a lead M, which is connected to the negative terminal i;of the differential amplifier l3, are continued and connected to adiiierential amplifier and mixer circuit (see Fig. 2). The bus 53 isdirectly connected to the control grid of a triode type vacuum tube BIand to the anode of a diode type tube 62. The anode of the tube 6i isconnected through a dropping resistor 63 to the positive bus 56 and thecathode of such tube is connected through a resistor 64 to a secondnegative bus 66 of the power supply (not shown). Also, a resistor 61 isconnected between the anode of the tube 6! and a grounded bus 88. A.second triode type vacuum tube H has the cathode thereof directlyconnected to the cathode of the tube 6! so that voltage changes acrossthe resistor '54 effect the operation of such tube. The control grid ofthe tube H is directly connected to the adjustable element of apotentiometer l2 which is series-connected with a resistor i3 betweenthe grounded bus 58 and a second positive potential bus '34 of the powersupply (not shown). The remaining connections to the tube ii are fromthe anode through a dropping resistor 16 to the positive bus 5 and toone end of a parallel resistancecapacitance coupling circuit Tl. Theother end of such coupling circuit 11 is connected to the control gridof a pentode type amplifier tube 85 and to the second negative bus 66through a resistor 82. The cathode of the tube BI is directly connectedto the grounded bus 68 and to the suppressor grid of the tube. Thescreen grid is suitably supplied with an operating voltage by a directconnection to the first positive bus 35. Further connections of the tube8i are from the anode through a dropping resistor 83 to the secondpositive bus '14 and directly to one end of a parallelresistance-capacitance coupling circuit 84. The other end of thecoupling circuit 84 is directly connected to the control grid of atriode type vacuum tube 55 and through a resistor '8'! to the secondnegative bus 66. The anode of the tube 86 is directly connected to thefirst positive bus 15 while the cathode is connected to the secondnegative bus 68 through a resistor 88. Such connections of the tube 86render such tube operative as a cathode follower and the cathode isconnected to an output terminal 9! which in turn is connected to thecontrol grid of the input tube 6! through a resistor {52.

The lead 55 is connected through a resistor as to the control grid of atriode type tube 91 which is connected to the cathode of a diode typetube 98. The anode of the triode type tube 9? is directly connected tothe first positive bus 16 while the cathode is connected through aseries-connected potentiometer 99 and resistor lfii to the firstnegative bus 48. The anode of the diode type tube $3 is connected to thejunction of two series-connected resistors !82 and H33 which togetherwith a potentiometer ifi i form a voltage divider between the groundedbus 68 and the second negative bus 66. The cathode of thepreviously-referenced diode type tube '52 is connected through alimiting resistor N16 to the adjustable element of the potentiometer 93.A final connection of the circuit is made directly from the grounded bus(iii to a second output terminal in! so that the voltages developedacross the two output terminals 9| and it? are output voltages of thecircuit.

Consider now the operation of a circuit, as described above, havingtwenty units ii so as to provide an output voltage waveform with twentyindependently adjustable points. Under such condition the difierentialamplifier i3 is adapted to amplify an input sawtooth of voltage so that,for example, the voltage between the terminals I6 and I8 is a sawtoothvoltage which varies from 0 to +400 volts and that between the terminalsi1 and I9 is a sawtooth voltage which simultaneously varies from 0 to400 volts. With such outputs from the differential amplifier i3, thevoltages of the two floating power supplies 2i and 3| are set for 400and 410 volts, respectively. The resistors 24 and 26, and 36 and 33 ofthe two voltage dividers are of such values that the units ll operate ina manner to be described hereinafter.

Consider now the operation of the first unit 45 when it is connectedbetween the two voltage dividers; i. e., the unit ii is connectedbetween the positive terminal 22 of the power supply 7.! and thepotentiometer 3G is connected closest to the negative terminal 32 of thepower supply 3|. For the example being described, the adjustable elementof the potentiometer 3%;- is set so that a voltage of +40 volts appearsat the cathode of the diode tube 43 and this voltage is with respect tonegative terminal 32 of the power supply 3!. From the foregoing it willbe apparent that, because the control grid of the tube 42 is coupled tothe positive terminal 22 of the power supply 2i, there will be no effectof the latter upon the operation of the unit iii being described. Now,as an output sawtooth wave of voltage occurs at the output of thedifferential amplifier IS the voltage at the control grid of the tube 42and the anode of the diode tube 33 increases while the voltage at thecathode of the diode tube 43 decreases. During the first 20 volt changein each of the outputs of the diiferential amplifier l3 the control gridof the tube 62 becomes increasingly positive so that conduction of thetube increases. At the same time the cathode of the diode tube 33 ismore positive than the anode and conduction of such tube prevented. Thetube 42 is connected as a cathode follower with suitable operatingpotentials being supplied and, therefore, the cathode follows thecontrol grid to apply an increasing positive voltage to the anode of thesecond diode tube it and to render the same conductive. creasinglyconductive as the voltage at the control grid increases, so then doesthe tube i l become increasingly conductive as current flows through theresistor 5i, potentiometer 52, and bus 53. Such is the operation of theunit a! during the time each of the outputs of the differentialamplifier l3 varies from G to volts.

At the time both outputs of the amplifier l3 have a value of 20 volts,it will be readily apa parent that the anode and cathode of the diodetube 43 have the same value of impressed voltage. Therefore, as thevoltages of the outputs of the amplifier 93 continue to change from 20to 40 volts, the anode of the diode tube M will become more positivethan the cathode so that the tube conducts by an increasing amount. Suchaction results in current flowing through the resistor as which opposesthe impressed voltage at the control grid of the tube 32. resistor is issuch that the tube 42 is not completely cut off until the ouptuts of thedifierential amplifier i3 reach values of 49 volts. Thus during the timethe outputs of the amplifier I3 change from 0 to 40 volts there isdeveloped a voltage across the cathode resistor 2-7 of the tube G2 whichchanges from zero to a maximum value and then to zero; i. e., asymmetrical back-toback sawtooth or triangular wave is developed. Thevoltage across the cathode resistor ll in turn controls the conductionof the second diode tube it and thereby the flow of current through thebus 53. Thereafter, as the output voltages of the differential amplifierit increases from 40 to 400 volts the tube remains in a nonconductingstate and the second diode tube 44 is cut off.

The second unit it is connected between the adjustable element of thepotentiometer 26 connected closest to the positive terminal 22 of theregulated power supply 2i and the adjustable element of the secondpotentiometer 35 connected at the end of the voltage divider nearest thenegative terminal 32 of the power supply 32. The adjustable element ofthe potentiometer 26 is adjusted to te point where the voltage is 20volts with respect to the positive terminal 22 of the power supply 25and similarly the adjustable element of the potentiometer 36 is adjustedto the point where th voltage is +60 volts with respect to the negativeterminal 32 of the power supply 3!. With potentials established inaccordance with the foregoing, it will be apparent that the second unitll will operate in the manner set forth for the first unit ll, butwithin the interval of 20 to 60 volts of the output of the differentialamplifier 13.

The following eighteen units All are similarly connected between the twovoltage dividers with the potentiometers 26 and 35 adjusted to providevoltages successively decreasing in the one instance and successivelyincreasing in the other. Such increase and decrease in voltage in eachcase being 20 volts so as to provide twenty independently adjustablepoints with the 400 volt of the output voltage of the differentialamplifier it.

Since the tube t2 becomes in- The value of the With the adjustableelements of the potentiometers 52 positioned at the center taps thereof,it will be readily apparent that a series of overlapping triangularwaves of current will be available at the bus 53. Each of suchtriangular waves has, in the example being discussed, an equal maximumvalue and an equal duration. Now, as set forth previously, the firstunit (if operates to draw a current which is linearly increasing to amaximum value during the first 20 volt change of the output of thedifferential amplifier i3 and linearly decreasing during the second 20volt change. Also during the second 20 volt change the second unit ifdraws a current which is linearly increasing to a maximum value andduring the third 20 volt change draws acurrent which is linearlydecreasing. The following units ll operate in similar manner so that thecurrent of the bus 53 starts at zero and at the end of the first 20 voltchange reaches a maximum value which is maintanied for the remainingperiod of the input voltage.

The bus 53 is connected to the control grid of the tube ti and thecircuit elements connected to such control grid have values which resultin a bias of +10 volts at the maximum values of current during the timeeach unit iii is conduc tive. A further connection to the control gridof the tube 5i comprises the diode tubes '52, triode tube 91, and diodetube 98. The purpose of the latter connection is to supply a negativevoltage which varies linearly from zero to 10 volts during the first 20volt change of the output voltage of the differential amplifier i3 andthen remains at 10 volts for the remainder of such output voltage. it isto be noted that the lead 5 which carries the voltage of the negativeterminal I? of the differential amplifier E3, is connected to thecontrol grid of the triode tube ill. The latter tube 9? is suitablyfurnished operating voltages so that the tube is normally conducting andcurrent flowing through the cathode circuit. The adjustable element ofthe potentiometer 95) is set so that the diode tube @2 is normallyconductive; that is, the cathode is posi' tive with respect to theanode. Now, as the out put voltage of the differential amplifier varieslinearly from 0 to 2 volts the triode tube becomes decreasinglyconductive in a proportional manner which lowers the voltage at theadjustable element of the potentiometer 9%, thereby making the diodetube 52 increasingly conductive. The values of the voltages applied andcircuit elements connected in the circuit are such that the voltage atthe control grid of the triode tube 6i, because of the action of thediode tube 62, varies from 0 to l0 volts during the aforesaid change inthe output of the differential plifier 53. The diode tube Q8 startsconducting when the control grid of the triode tube ill is biased at 20volts and limits such bias voltage to that value. From the foregoing itwill be apparent that the voltage of the control grid of the triode tube5! will be zero for the entire time of the incoming signal.

Having established a condition of zero bias at the control "rid of thetriode tube 6i for the duration of the incoming voltage, it is necessaryto provide a differential output for the purposes of the invention. Theamplifier circuit comprising the tubes bl, ii, 3i, and is such that 106%of the voltage developed at the cathode of the final tube 85 is fed backto the input. Consider the action of such amplifier when the adjustableelement of the potentiometer 52 in the first unit is varied to increasetheresistance' of the'cathode circuit of the diode tube 44: The resultof such variation is to decrease. the rate of conductance of the tube 14and the maximum value of current flow when the outputivoltage of thediiierential amplifier reaches 20volts. The bias of the triode tube BIis altered by the difierence between the negative bias supplied from thediode tube 52 and decreased positive bias from the unit 3!. Phenet'resultis a negative going bias at the control grid of the tube 61,thereby causing a similar voltage to appear across the cathode resistertl. Since the'resistor 64 is also connected to the cathode of the tube H,the negative going voltage .thereacross increases conduction ofthetube'and'therebydecreases the anode voltage. Since the pentode tube85 is connected to amplify the. anode voltage of the tube l i, anincreasing voltage is applied to the control grid of thecathode'foll'ower'tube 86; The cathode voltage of the tubefsfi'followsthe control grid voltage and so a positive going voltage isfed back to the control grid of the triode. tube "3i and directly tothe. output terminal 9!. The value of the cathode resistor 88 isselected so that the cathode of the tube 80 swings about zero voltagewith respect to ground depending uponthe amount of current flowingthrough the tube.

Applying the same operating principles, itis apparent'that, when theadjustable. element of the potentiometer 52 is moved to decrease theamount of resistancein the cathode circuit of the diode tube 44', agreater maximum value of current flow is reached at the 20 volt pointor" the voltage of'the. differential amplifier :3. Such change increasesthe grid bias of the tube t: and results in a negative: voltage at theoutput terminal 9!.

Also, it is to be noted that each of the other units 4| may be similarlyoperated to vary the maximum current drawn by the individual unit andthereby adjusts the voltage waveform at the output terminals 9| and.Hll' between the range of +10 to -10 volts; As. indicated previously,the adjustment or one of the units 4| changes the voltage of the outputat the terminals i and it? at the point of maximum'conduction withouteliecting the voltages determined by the other units' i, but the slopeof the output voltage between such adjusted point and the preceding, aswell as following, points is varied. In such maimerthen therehas beendescribed a voltage Waveform generator having great flexibility toaccomplish the objects-of the invention.

A list of values and types, where applicable, of the various'elements ofthe invention will be set forth hereinafter. Such list will be inaccordance with the twenty-point waveform gener" ator as described indetail in the foregoing and should not be construed as limiting in anyrespect.

24. Resistor .100 ohms 26. Resistor 1000 ohms as. Resistor 100 ohms 36.Resistor 1000 ohms 52. Tube, type 12AT7' s3. Tube, type 6AL5 i l. Tube,type /z 6AL5 il. Resistor 150K ohms t9. Resistor 1 megohm i. Resistor Kohms 52. Resistor 50K ohms 6i. Tube, type 12AY'7' S2. Tube, type /g6AL5B3. Resistor 47K'ohms' 8 Resistor 300K ohms Resistor 1 megohm Tube, type12AY7 Resistor 5K ohms Resistor 600K ohms Resistor'TK ohms Resistor 1.2megohm and Capacitor 10 micro-microfarad Tube, type 6AU6 Resistor 6.2megohm Resistor K ohms Resistor 1.2 megohm and Capacitor 10micro-microfarad Tube, type 12AU7 Resistor 6.2 megohm Resistor 30K ohmsResistor 12K ohms Tube, type A 12AU7 Tube, type 6AL5 Resistor 5K ohmsResistor 75K ohms Resistor 50?: ohms I03. Resistor 1200 ohms 05.Resistor 1K ohms I90. Resistor 13K ohms It will be apparent fromconsideration of the foregoing that the invention is useful r'crapplications other than the one outlined earlier with respect to thefrequency control or" the accelerating voltage of a particleaccelerator. In such respect it is desired to point out that the slopeof the incoming signal may be varied to alter the interval betweenselected adjustable points of the waveform being developed therebyfurthering the flexibility of the invention.

While the salient features of the invention have been set forth indetail with respect to one embodiment it will be apparent that no" 'ousmodifications may be made within the 5p scope of the invention, and itis therefore not desiredto limit the invention "to the exact detailsshown and described except insofar as they may be defined in thefollowing claims.

What is claimed is:

i. In a circuit for developing a voltage waveform havin a plurality ofadjustable pcin response to an input voltage wave, the co tioncomprising a differential amplifier ing positive and negative outputvoltages in re sponse to an input voltage with the pola ity be ing withrespect to g ound and the "av rm of such voltages being substantiallythe same, a plurality of triode tubes connected as cathode followers,means connected to said triode tubes to supply operating voltages, aplurality of series circuits including a resistor and a diode with thejunction therebetween respectiveiy connected to the control grids ofsaid triode tubes, said. resistor of one of said series circuits beingcon" nected directly to the positive output of amplifier and the cathodeof said diode being connected to thenegative terminal of said amplifierthrough an element having a fixed value of volta e opposing the outputvoltage or? said amplifier, the remainder of said series circuits beingsuccessively connected in a similar manner with an element having avalue of voltag ".iere-- across which is one-half that of said fixer?vaiue inserted in opposition in the connections at either end, aplurality of variable impedances respectively connected at one end. tothe cathodes of said triode tubes and at the other end to other, anegative feedback amplifier having a cathode follower output, the inputof said negative feedback amplifier being connected to the 64; 61. ll.T2. 13. 78. 17.

86. 87. 88. 92. 9.1. 93. 99. ifil. Hi2.

common connection of said variable impedances, bias means connected tothe input of said negative feedback amplifier for canceling the voltageimpressed when said variable impede-noes are set at mid-value, andoperating voltages connected to said cathode follower output such thatthe cathode thereof operates above and below ground potential inaccordance with the settings of the individual variable impedances.

2. In a voltage waveform generator, the combination comprising adiiferential amplifier developing positive and negative output voltagesin response to an input voltage with the polarity being with respect toground and the waveform of such voltages being substantially the same, afirst floating power supply having the positive terminal connected tothe positive output of said amplifier, a first voltage divider having aplurality of variable voltage points connected across said first powersupply, a second floating power supply having the negative terminalconnected to the negative output of said amplifier, a second voltagedivider having a plurality of variable volt age points connected acrosssaid second power supply, a plurality of cathode follower tubes havingthe anode and cathode circuits connected to a source of operatingvoltages, a plurality of first diodes having the anodes respectivelyconnected to the control grids of said cathode follower tubes, aplurality of second diodes having the anodes respectively connected tothe oathodes of said cathode follower tubes, a plurality of currentlimiting resistors, one of which is connected between the control gridof the first of said cathode follower tubes and the positive terminal ofsaid first power supply and the remainder of which are respectivelyconnected between the control grids of successive cathode follower tubesand successive variable voltage points of said first voltage divider.the cathode of the first of said first diodes being connected to thefirst variable point of said second voltage divider closest to thenegative terminal of said power supply and the cathodes of the remainingcathode follower tubes being respectively connected to successivevariable voltage points of said second power supply, a plurality ofvariable resistors respectively connected to the cathodes of said seconddiodes and having the adjustable elements thereof connected together, anegative feedback amplifier having a cathode follower output, the inputof said negative feedback amplifier being connected to the commonconnection of said variable resistors, bias means connected to the inputof said negative feedback amplifier for canceling the voltage impressedwhen said variable resistors are set at mid-value, and operatingvoltages connected to said cathode follower output such that the cathodethereof operates above and below ground potential in accordance with thesettings of each of said variable resistors.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,409,229 Smith, Jr., et a1. Oct. 15, 1946 2,486,391Cunningham Nov. 1, 1949 2,488,297 Lacy Nov. 15, 1949 2,529,666 SandsNov. 14, 1950 2,541,039 Cole Feb. 13 1951

